L13 - Early Human Development Flashcards
Result of embryogenesis
- patterning
- definition of major acids
- definition of three germ layers (via gastrulation)
- rudiments of major organs established
Patterning
Cells acquiring identity in space and time
Major axis
Anterior/posterior
Dorsal/ventral
Three germ layers
- ectoderm (outside)
- mesoderm (between)
- endoderm (inside)
Ectodermal contributions
- all nervous tissue
- epithelium of integumentary, respiratory, digestive
(Skeletal - pharyngeal cartilage)
Mesodermal contributions
- All of:
- skeletal
- muscular
- cardiovascular
- lymphatic
Endodermis contributions
- digestive system (gut)
- respiratory epithelium (along with ectoderm)
Ecto/mesodermal contributions
- integumentary (epidermis vs. dermis/hypodermis)
Meso/endodermal contributions
- urinary (kidneys vs. bladder)
- reproductive (gonads/ducts vs. stem cell)
All germ layer contributions
Endocrine
Arrest points in oogenesis
- Prophase I (resumed during puberty)
- Metaphase II (resumed after fertilisation)
Polar bodies
Other daughter cells from meiosis that are not fertilised as all cytoplasm apportioned to one cell as it divides
- eventually gets degraded)
Path of sperm cell
- corona radiata (cells from ovary itself)
- zone pellucida
- plasma membrane of secondary oocyte
- cytoplasm of secondary oocyte
Pronuclei
Nucleus of gametes (haploid)
Cleavage
Series of relatively rapid mitotic cell division (24hrs for each cell division in humans)
Zone pellucida function
- fibrous
- prevents early implantation in Fallopian tube (which would lead to ectopic pregnancy) where a placenta cannot be formed thus no nutrient/waste exchange = death
Ectopic preganancy
Implantation of zygote outside uterus
Resulting cells from cleavage
Blastomeres
Cleavage features
Overall volume/mass of egg doesn’t increase
- instead, cells become progressively smaller as they split without growth (rapid cell division)
Blastocyst
Mammalian blastula with trophoblast & pluripotent inner cell mass instead of no inner cell mass and pluripotent blastomere/blastoderm
Morula vs. blastocyst
- loosely associated vs. tightly packed cells
- absence vs. presence of inner cavity
Blastocyst formation
Morula hatches our of zona pellucida which allows the blastocyst to be sticky and thus implant into uterus wall
Embryoblast
Aka inner cell mass
- pile of cells inside blastocyst that give ruse to embryo (result of compaction)
Blastocyst cavity
Fluid-filled (H2O enters via osmosis)
Trophoblast
Give rise to placenta + other supporting tissue
If 2 eggs released
Potentially 2 fertilisation events
= may give rise to fraternal twins
Cleavage/blastulation timeline
Day 1: two cell Day 2: four cell Day 4: morula Day 5: blastocyst Day 6: implantation
Types of trophoblasts
- syncytiotrophoblast: part of embryo that gives rise to placenta
- cytotrophoblast
Trophoblast function
- require/use enzymes that allow embryo to burrow deep into endometrium
- promote uterine endometrium to thicken
- release human chorionic gonadotropin hormone (detected by preganancy tests)
Endometrium
Lining of the uterus
Importance of placenta
Critical as it is the connection to the female and thus us a supply of nutrients and way of getting rid of waste products
Bilaminar embryonic disc composition
- hypoblast: endoderm
- epiblast: ectoderm
Result of differentiation of inner cell mass
(Mesoderm established from gastrulation
Gastrulation time
End of 2 weeks post-fertilisation
Amnion/amniotic cavity
Cavity formed by ectoderm
Yolk sac
Cavity formed by endoderm
Connecting stalk
Connects amniotic cavity to cytotrophoblast of blastocyst
- precursor to umbilical cord
Primitive streak
Groove that determines embryo’s right/left symmetry as it develops
Formation of mesoderm
- 16 days post fertilisation
- derived from ectoderm
Invagination
Movement of cells to form primitive streak
Cells from inner cell mass:
- divide
- change shape
- become motile
- rearrange to form flat disc with 3 distinct layers = CELL DIFFERENTIATION BEGUN
Embryonic folding time
22 days - 28 days post fertilisation
4th week
Embryonic folding
- gives rise to 3D embryonic shape
- allowed by cell movement (curving), proliferation, changes in cell shape = dynamic
- patterning already taken place
Organogenesis
Formation of organs
Neural tube
Differentiated ectoderm
Notochord
Differentiated mesoderm
Differentiated cells
Have limited replicative potential/division
Stem cells
Undifferentiated cell of a multicellular organism capable of giving rise to indefinitely more:
- cells of same type (retain stem-cell properties)
- other daughter cells from which certain other types of cells arise by differentiation
Replace themselves
Purpose of stem cells
Growth, renewal, repair
Transient amplifying cells
Intermediate form
- have some replication potential
Linage-restricted progenitor cells
Limited ability to renew
Stem cell hierarchy
Most potent
- totipotent: zygote (embryo AND placenta)
- pluripotent: inner cell mass of blastocyst (only embryo)
- multipotent: particular tissue or organ
- nullipotent/unipotent: not capable of giving rise to other cell types
Clinical utility of stem cells
For long lasting skin grafts: keratinocyte stem cells need to be gene-edited
Keratinocytes
Fulfil need for source of stem cells in skin
- ability to keep diving and give rise to differentiate keratinocyte
- protected in stem cell niche which have signals to tell them to keep dividing
- unipotent stem cells allow for constant renewal
